Solar energy device for electricity and heating

ABSTRACT

A solar energy collector produces electricity and heat using an optically transparent vessel containing one or more photovoltaic cells and a liquid that substantially fills the vessel. The vessel has a top with a flat exterior surface and a bottom with a concave exterior surface that is coated on the outside with a reflective material. Solar radiation traveling through the top of the vessel into the liquid and through the bottom strikes the reflective material on the outside of the vessel and is reflected back through the bottom, into the liquid and to a focal line adjacent to the interior surface of the top. Cooled liquid is fed into the vessel through an entry port and heated liquid is removed through an exit port. One or more photovoltaic solar cells are located adjacent to the interior surface of the top aligned with the focal line.

FIELD OF INVENTION

In the field of solar energy conversion, a device that converts themajority of solar energy collected by it into electricity and heat andis efficient, low cost, and easy to manufacture.

BACKGROUND OF THE INVENTION

The invention is a solar energy collector that produces electricity andheat using an optically transparent vessel containing photovoltaic cellsand substantially filled with a non-conducting, optically transparentliquid, used for removing heat.

Devices that produce both electricity and heat from concentrated solarenergy are known. However, such devices have been disclosed primarilyusing concentrated refracted solar energy, which are less effective inconcentrating solar radiation. Concentrated refracted solar energydevices typically require a liquid with a high refractive index and asun-tracker capable of orienting the device along two axes: the verticalorientation of the major axis, which is in effect rotation of the deviceabout its minor axis; and the horizontal orientation of the minor axis,which is in effect rotation of the device about its major orlongitudinal axis.

Concentrated refracted solar energy involves passing solar radiationthrough a lens to focus it and thus concentrate its effect. The presentdevice does not use refracted or lens-concentrated solar energy. Rather,the present invention utilizes concentrated reflected solar energy. Byso doing, the present invention can produce a higher concentration ofsunlight with simple shapes, especially when a parabolic shape is usedfor the bottom exterior surface. Also, the present invention requiressun tracking only along a single axis, namely, rotation around itslongitudinal axis. No complex two-axes tracking is required. Once thelongitudinal axis of the present invention is aligned along theeast-west direction, there is no need for large directional adjustment,only “fine tuning,” i.e., smaller and more precise adjustment is neededonly for any seasonal change or slight misalignment of the device.

To produce a comparable concentration, a refractive device would need toa complex configuration with multiple lenses. With a simple design, thepresent invention improves efficiency while reducing the weight andquantity of material often associated with refractive devices. Overall,the present invention has advantages in lower-cost manufacture, ease ofmanufacture and broader application potential for backfitting toexisting buildings.

The apparatus of the present invention concentrates sunlight viareflection, that is, the area of the sunlight used for the production ofelectricity is greatly reduced from the unconcentrated area ofillumination by the sunlight. This reduced area of sunlight enables useof fewer solar cells to achieve the same electrical output for the solarenergy impinging on the apparatus. Thus, it either enables use of fewercells for the same electrical output, or for a comparable cost, itenables the use of high-efficiency photovoltaic cells, such asmulti-junction solar cells. When a high-efficiency photovoltaic cell isutilized, the invention can translate to a more efficient device with alower cost per unit of power.

The present invention combines a photovoltaic cell and a means for heatextraction in a unique arrangement to promote efficient operation ofboth means for extracting useful energy from solar radiation. It isknown that a photovoltaic cell can produce electricity from sunlight andits efficiency can be maximized by maintaining the cell as close toambient temperature as reasonably achievable in the presence ofconcentrated sunlight. The key to higher efficiency is to provide solarcell temperature regulation while at the same time enabling theextraction of the heat energy created by the sunlight. Therefore, thepresent invention enables a reflecting solar concentrator to beeffective in producing electricity from one or more solar cellsmaintained near ambient temperatures and to easily extract the heatenergy.

An alternative embodiment of the present invention employs solartracking to rotate the apparatus so that solar radiation enterslatitudinally perpendicular to the apparatus. Solar tracking is wellknown in the art. However, a specific means for achieving solar trackingis described for the present invention. Essentially, the vessel used inthe apparatus is rotated about its longitudinal axis to achievefocusing. Two parallel solar cells on the inside top of the vessel areused to measure variation in relative radiation intensities and therebysend signals to rotate the vessel.

DESCRIPTION OF PRIOR ART

The prior art in this category relates primarily to concentratedrefracted solar energy and is also different in a number of other ways.An example is U.S. Pat. RE30,584, which teaches an optical concentratorand cooling system in which a photovoltaic cell array is immersed in aliquid coolant inside an elongated tube having a curved transparentwall, which is a lens, to focus incident radiation by refraction on aphotovoltaic cell array. To operate effectively, this tube must beadjusted along two axes with direction of the sunlight, that is, so thatthe sunlight is longitudinally perpendicular, and latitudinally alignedto its axis of symmetry. Two-axes adjustment is needed because ifsunlight is not perpendicular to the longitudinal axis of the tube, thenlatitudinally, the governing refraction equation k=sin (α)/sin (β) is nolonger true and focusing is less effective.

While the present invention uses a coolant surrounding a photovoltaiccell, the present invention is different in that it does not concentratethe solar energy via refraction. Thus, the functionality of the presentinvention is via a completely different mechanism, which is reflectionrather than refraction. This means that because refraction is notimportant, there is no limitation on the refractive index of the liquidcoolant. In contrast, the '584 patent requires that the coolant haverefractive index suitable for concentrating the incident radiation ontothe photovoltaic cell array. With typical refractive indices ofavailable liquids, calculation shows that no more than a factor of 5concentration of incident solar energy can be achieved with the '584device. Additionally, the present invention uses an external reflectivecoating not found in this type of application. With a parabolicreflective shape of the present invention, it is a mathematicalpossibility to focus the sunlight to arbitrarily small size.

An example can be given of the weight savings of the present inventioncompared to a refractive device described by the '584 patent. Assumecomparison of devices using the same concentration factor (e.g., x100,which is difficult to achieve with refractive device) and same solarcell width (e.g., 1 mm), the refractive device would have the diameterof 10 cm, and the parabolic reflective device of the present inventionwould have a width of about 10 cm but a height of only about 25 mm (1inch). This translates to a substantial savings in material and weight.

Accordingly, the present invention will serve to improve the state ofthe art by providing a highly efficient device for producing electricityand heat from solar radiation that substantially reduces the weight andmaterial previously needed for such purposes. Reduced weight andmaterial translates to broader application potential to existingbuilding structures. A reduced weight solar energy device alsotranslates to lower manufacturing costs. Additionally, the simple designof the present invention enables ease of manufacture that contributes toreducing costs per unit of power produced.

BRIEF SUMMARY OF THE INVENTION

A solar energy collector produces electricity and heat using anoptically transparent vessel containing one or more photovoltaic cell.The vessel is substantially filled with a non-conducting, opticallytransparent liquid, such as silicon oil, used for removing heat. Thevessel wall has a refractive index about the same as the liquid. Thevessel is shaped in cross-section to have a top with a flat exteriorsurface so that solar radiation passing through the top enters thevessel in substantially parallel rays. The vessel has a bottom with aconcave exterior surface, preferably a parabolic shape, which is coatedon the outside with a reflective material. This shape enables solarradiation traveling through the top of the vessel into the liquid andthrough the bottom to strike the reflective material on the outside ofthe vessel and be reflected back through the bottom, into the liquid andto a focal line adjacent to the interior surface of the top. The vesselhas an entry port to enable introduction of cooled liquid into thevessel and an exit port to enable removal of liquid heated by solarradiation. A photovoltaic solar cell is located adjacent to the interiorsurface of the top aligned with the focal line. A tracking device toalign the device with the sun's movement may be used.

BRIEF DESCRIPTION OF THE DRAWINGS

The reference numbers in the drawings are used consistently throughout.New reference numbers in FIG. 2 are given the 200 series numbers and inFIG. 3 are given 300 series numbers.

FIG. 1 is a perspective of a preferred embodiment of the invention.

FIG. 2 is a sectional view of an alternative preferred embodiment of theinvention.

FIG. 3 is a side view of a preferred embodiment of the invention mountedon a sun tracker.

FIG. 4 is a cross-sectional view of the vessel used in the preferredembodiment of the invention mounted on a sun tracker.

DETAILED DESCRIPTION

In the following description, reference is made to the accompanyingdrawings, which form a part hereof and which illustrate severalembodiments of the present invention. The drawings and the preferredembodiments of the invention are presented with the understanding thatthe present invention is susceptible of embodiments in many differentforms and, therefore, other embodiments may be utilized and structuraland operational changes may be made without departing from the scope ofthe present invention.

FIG. 1 shows a perspective of a preferred embodiment of the apparatus(100) for collecting solar radiation for electricity production and heatand FIG. 2 shows a cross section of a squatter preferred embodiment ofthe apparatus (200). Each preferred apparatus comprises liquid (250), avessel and a photovoltaic cell (140).

Sunlight would enter the vessel through the wall at the flat exteriorsurface of the top (110), pass through a liquid (250) that substantiallyfills the vessel, pass through the wall at the bottom (120), and strikea reflective material (130) that coats the concave exterior surface(221) of the wall at the bottom (120), which is preferably parabolic inshape. The sunlight would then be reflected back through the wall at thebottom (120), pass through the liquid (250) and onto one or more solarcells, that is a photovoltaic cell (140), located on the wall at the top(110) along a focal line of the concave shape.

The liquid (250) is non-conducting so that it does not adversely affectthe production of electricity in the normal operation of thephotovoltaic cell (140). The liquid (250) is optically transparent sothat sunlight can pass through the liquid (250) to the reflectingmaterial (130) and on its way back to the photovoltaic cell (140). Theliquid (250) serves as a heat sink for solar radiation and a means tocool the photovoltaic cell (140). A liquid meeting these requirements issilicon oil. To reduce weight in transport and to ease installation, theliquid may be added as a last step in installation.

The vessel wall, composed of the top (110) and bottom (120), isoptically transparent so that solar radiation can pass through the wall.Optically transparent glass or plastic materials are well known for thistype of application. The vessel wall preferably has a refractive indexabout the same as the liquid (250) so that the light is not refracted orbent when it passes from the wall to the liquid (250).

The wall at the top (110) has a flat exterior surface (212) such thatsolar radiation passing through the top enters the vessel insubstantially parallel rays. The interior surface (211) of the wall atthe top (110) is shown also as flat, but it need not be flat in allapplications. When the refractive index of the wall and the liquid (250)is the same, the shape of the top interior surface does not affectoperation of the device.

The wall at the bottom (120) has a concave exterior surface (221). Theinterior surface (222) of the wall at the bottom (120) is shown also asconcave but it need not be concave in all applications. The concaveexterior surface (221) is coated with a reflective material, ormirror-like material, so that parallel rays of solar radiation travelingthrough the wall at the bottom (120) will strike the reflective materialand be reflected back through the wall at the bottom (120) to a focalline adjacent to the interior surface (212) of the wall at the top(110).

This embodiment has an entry port (170) to enable introduction of cooledliquid (250) into the vessel. This embodiment also has an exit port(160) to enable removal of liquid (250) heated by solar radiation. Theseports enable liquid (250) to be introduced at a cold temperature andremoved at an elevated temperature. Once removed, liquid at elevatedtemperature may be piped to a heat exchanger to cool it forreintroduction into the vessel. Examples of a useful heat exchanger area system for space heating, a water tank inside a building or a radiatorin a house to directly heat the house. These examples are well known inthe art.

The ports also enable more than one vessel to be connected in series orparallel in a coolant system distribution system. An example of aconnection in series is connecting the exit port of a first vessel tothe entry port of a second vessel. An example of a connection inparallel is connecting the first and second vessel entry ports to acommon feeder pipe and the first and second vessel exit ports to acommon suction pipe. To maintain as low-cost and as light a package aspossible, flexible tubing can be used to connect multiple vesselstogether. A casing may be used to house multiple vessels so connectedand each casing would then constitute a solar panel module.

The photovoltaic cell (140) in this embodiment is located adjacent tothe interior surface (212) of the top (110) aligned with the focal lineof the concave exterior surface (221) of the exterior of the wall at thebottom (120). If multiple vessels are involved in an application, one ormore photovoltaic cells in each vessel can be electrically connected inseries or parallel to vary the current or voltage obtainable from thephotovoltaic cells. Such connections are well known in the art.

FIG. 3 shows an alternative embodiment of the invention that uses ameans for rotating the apparatus such that sunlight (310) impingessubstantially latitudinally perpendicularly to the flat exterior surface(211) of the wall at the top (110).

FIG. 4 shows a cross section of the vessel used in the embodiment shownin FIG. 3.

The means for rotating preferably includes a worm gear (300) operated bya servo-motor (320). Each vessel is attached to a gear (310) thatengages the worm gear (300). Rotation of the worm gear turns all of thevessels at once about the axis of the gear. This means for rotating doesnot change the angle of the long axis of the vessel with respect to theground, which is fixed upon installation. With the alignment of the longaxis of the vessel to the east-west direction, the rotation around thelongitudinal axis adjusts for the seasonal changes in the altitude ofthe sun and any daily adjustment needed due to the slight misalignment.Alternatively, two or more solar cells (341 and 342) are used in thesame vessel in the side-by-side fashion. Their relative outputintensities response to position is used to provide the tracking signalfor fine tuning the rotation of the vessel for maximum output. Anexternal directional sensor of the position of the sun is added when alarger range of adjustment is desired.

The means for rotating may include other tracking devices that are wellknown in the art. These included fully self contained devices thatchange the orientation of the apparatus. All that need be done toutilize such an alternative sun-tracking device is to mount one or moreof the apparatus (100) on the means for rotating (300).

The above-described embodiments including the drawings are examples ofthe invention and merely provide illustrations of the invention. Otherembodiments will be obvious to those skilled in the art. Thus, the scopeof the invention is determined by the appended claims and their legalequivalents rather than by the examples given.

What is claimed is:
 1. An apparatus for collecting solar radiation forelectricity production and heat comprising: (a) a liquid that isnon-conducting and optically transparent; (b) a vessel substantiallyfilled with the liquid comprising, (i) a wall, said wall being opticallytransparent and having a refractive index about the same as the liquidand wherein said wall is shaped in cross-section to comprise a tophaving a flat exterior surface such that solar radiation passing throughthe top enters the vessel in substantially parallel rays, and, a bottomhaving a concave exterior surface that is coated with a reflectivematerial such that parallel rays of solar radiation traveling throughsaid bottom and striking the reflective material is reflected backthrough said bottom to a focal line adjacent to the interior surface ofthe top, and, (ii) an entry port to enable introduction of cooled liquidinto the vessel; (iii) an exit port to enable removal of liquid heatedby solar radiation; and, (c) a photovoltaic solar cell located adjacentto the interior surface of the top aligned with the focal line.
 2. Theapparatus of claim 1 wherein the liquid is silicon oil.
 3. The apparatusof claim 1 wherein the concave exterior surface is parabolic.
 4. Theapparatus of claim 1 further comprising a means for rotating theapparatus such that sunlight impinges substantially latitudinallyperpendicularly to the flat exterior surface of the top.